Closed loop control is often used to manage the speed of machine transmission outputs, excavator swing platforms, and other speed-controlled machine elements. In general terms, such closed loop control operates by minimizing a difference between a desired speed and an actual speed of the element in question. In particular, the actual speed of the controlled entity is fed back to a controller which implements a PID (proportional-integral-derivative) process to derive a torque or torque command, which, when applied, will reduce the difference between the actual speed and the desired speed.
The controller will typically use three parameters to control the gain on the proportional, integral, and derivative stages respectively. While higher gains initially result in a more rapid response to speed change inputs, the gains needed to provide sufficient responsiveness often result in instability such as continuous overshooting or ringing. These problems are exacerbated in systems having inherent mechanical backlash and/or significant communication or processing delays. Thus, a stable speed control algorithm for such a system typically requires more subdued gains to yield a stable system. However, while stability can be achieved, the resultant system is often sluggish in responding to operator control inputs. This can lead to operator impatience and dissatisfaction, and in some cases, may also result in operator errors and inefficiencies.
With respect to the conversion of the swing function of excavator machines from hydraulic drive to electric drive, the modification of the electric motor function to replicate the behavior of a hydraulic swing function has been addressed in at least one reference. See, for example, US Patent Application 20120283919, entitled “Electric Swing Drive Control System and Method.” In that application, the problem of braking the swing platform using the electric drive is discussed, and a method is disclosed for braking the swing motion at a substantially constant rate when a command signal indicates zero desired swing speed. However, this technique does not address the need to provide responsive behavior during an increase in swing speed.
The present disclosure is directed to a system that may exhibit numerous distinctions over prior systems. However, it should be appreciated that any such distinction is not a limitation on the scope of the disclosed principles or of the attached claims except to the extent expressly noted. Additionally, the discussion of any problem or solution in this Background section is not an indication that the problem or solution represents known prior art. For readers interested in a full and accurate understanding of the underlying feedback control theory and its limitations, numerous volumes on the subject are publicly available. This Background section is also too brief to fully and accurately describe the referenced patent application, and as such, the above characterization of the application is not itself prior art. Interested reads are referred to the application itself.